question_answer

The radioactivity of a sample is \[{{R}_{1}}\] at instant \[{{T}_{1}}\] and \[{{R}_{2}}\] at instant \[{{T}_{2}}\]. If the mean life of the specimen is T, the number of atoms that have disintegrated in the time \[({{T}_{2}}-{{T}_{1}})\] is :-

A)  \[{{R}_{1}}{{T}_{1}}-{{R}_{2}}{{T}_{2}}\]      

B)  \[{{R}_{1}}-{{R}_{2}}\]

C)  \[\frac{\left( {{R}_{1}}-{{R}_{2}} \right)}{T}\]    

D)  \[({{R}_{1}}-{{R}_{2}})\,T\]